A vacuum manipulating device of this type is known. The known device comprises a control element in the form of a pivotable control flap, which can be manually pivoted into the one or the other direction for unblocking, or respectively blocking an opening. In the non-actuated state of the control flap it should take up a defined position, which partially unblocks the opening, so that a defined poise is set by means of a suitable vacuum in the interior of the suction device and in the lifting hose. To take up this position, the control flap is prestressed by means of two springs acting in opposite directions, whose equilibrium defines the neutral position of the control flap and thus the poise.
However, in connection with this known vacuum manipulating device it has been shown to be disadvantageous in that the neutral position of the control flap depends on whether previously the control flap had been opened farther or closed farther. The cause of this is the frictional force acting between the control flap and a wall constituting the opening. Depending on the direction from which the control flap is pulled in the neutral position by the action of the two springs, the frictional force appearing here acts in the opposite direction. The poise, i.e. the neutral position of the control flap therefore is not unequivocally defined and cannot be reproducably attained.
A vacuum manipulating device, which is somewhat different from that noted above, is also known from European Patent EP 0 590 554 A1, wherein the opening, which can be unblocked, or respectively blocked by the control flap is always completely closed by the action of a single spring when the control flap is not actuated. The poise is created by a throttle device, which is separate from this and which acts on a further opening.